Respectability's a double-edged sword as it manifests in the experimentalists of yesteryear; Tortoise were last heard unabetted in 2004 honing their much-admired template almost to extinction with It's All Around You, a record that was refined and considered but verged on a kind of cerebral muzak at times.

Before post-rock transmuted into a genre reserved for Games Workshop enthusiasts of an artistic bent, the Chicagoan collective's 1996 platter Millions Now Living Will Never Die established them as giants of the scene, but since then they've largely eschewed dramatic recastings of the mould in favour of ever-clearer enunciations of their signature sound.

Finally, it seemed as though the mould was starting to cast them, as the well-spoken bores of assiduous, semi-improvisational rock - what, then, of the 2009 model, now settled in the same five-man line-up for over a decade? In fact, Beacons Of Ancestorship confounds expectations easily by relocating a sense of joy in eclecticism; trading off a little of the old tonal acumen for a bracing performance of genre-touristic brio.

The reference points are not generally new - '90s IDM on 'Gigantes', chintzy prog on 'Minors', mathy rumbling on 'Yinxianghechengqi'- but the manner of their execution is suddenly less restrained. The latter track comes careening out of leftfield with skronky, subterranean vigour, while 'Prepare Your Coffin' sounds like early Stereolab at a shotgun wedding in Vegas - pretty righteous stuff, then.

Somewhat less familiar are 'The Fall Of Seven Diamonds Plus One''s bossa nova spaghetti western - somewhere between Morricone and Young Marble Giants - and the slipping, sliding digital stew of 'Monument Six One Thousand', apparently conceived of in tribute to the late J Dilla.

That its quality is uneven in the end hardly seems to matter. It's as if, realising their judiciously timed bon mots are no longer having the desired effect on the present company, Tortoise have started hurling themselves about the room in the most amusing manner possible. And suddenly they're right back on top again.